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  <div class="section" id="context-variables-objects">
<span id="contextvarsobjects"></span><h1>上下文变量对象<a class="headerlink" href="#context-variables-objects" title="永久链接至标题">¶</a></h1>
<div class="versionchanged" id="contextvarsobjects-pointertype-change">
<div class="admonition note">
<p class="admonition-title">注解</p>
<span class="versionmodified changed">在 3.7.1 版更改: </span><p>在 Python 3.7.1 中，所有上下文变量 C API 的签名被 <strong>更改</strong> 为使用 <a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyObject</span></code></a> 指针而不是 <a class="reference internal" href="#c.PyContext" title="PyContext"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyContext</span></code></a>, <a class="reference internal" href="#c.PyContextVar" title="PyContextVar"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyContextVar</span></code></a> 以及 <a class="reference internal" href="#c.PyContextToken" title="PyContextToken"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyContextToken</span></code></a>，例如:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="c1">// in 3.7.0:</span>
<span class="n">PyContext</span> <span class="o">*</span><span class="nf">PyContext_New</span><span class="p">(</span><span class="kt">void</span><span class="p">);</span>

<span class="c1">// in 3.7.1+:</span>
<span class="n">PyObject</span> <span class="o">*</span><span class="nf">PyContext_New</span><span class="p">(</span><span class="kt">void</span><span class="p">);</span>
</pre></div>
</div>
<p>详情请参阅:issue: ' 34762 '。</p>
</div>
</div>
<div class="versionadded">
<p><span class="versionmodified added">3.7 新版功能.</span></p>
</div>
<p>本节深入介绍了 <a class="reference internal" href="../library/contextvars.html#module-contextvars" title="contextvars: Context Variables"><code class="xref py py-mod docutils literal notranslate"><span class="pre">contextvars</span></code></a> 模块的公用 C API。</p>
<dl class="type">
<dt id="c.PyContext">
<code class="sig-name descname">PyContext</code><a class="headerlink" href="#c.PyContext" title="永久链接至目标">¶</a></dt>
<dd><p>用于表示 <a class="reference internal" href="../library/contextvars.html#contextvars.Context" title="contextvars.Context"><code class="xref py py-class docutils literal notranslate"><span class="pre">contextvars.Context</span></code></a> 对象的 C 结构体。</p>
</dd></dl>

<dl class="type">
<dt id="c.PyContextVar">
<code class="sig-name descname">PyContextVar</code><a class="headerlink" href="#c.PyContextVar" title="永久链接至目标">¶</a></dt>
<dd><p>用于表示 <a class="reference internal" href="../library/contextvars.html#contextvars.ContextVar" title="contextvars.ContextVar"><code class="xref py py-class docutils literal notranslate"><span class="pre">contextvars.ContextVar</span></code></a> 对象的 C 结构体。</p>
</dd></dl>

<dl class="type">
<dt id="c.PyContextToken">
<code class="sig-name descname">PyContextToken</code><a class="headerlink" href="#c.PyContextToken" title="永久链接至目标">¶</a></dt>
<dd><p>用于表示 <code class="xref py py-class docutils literal notranslate"><span class="pre">contextvars.Token</span></code> 对象的 C 结构体。</p>
</dd></dl>

<dl class="var">
<dt id="c.PyContext_Type">
<a class="reference internal" href="type.html#c.PyTypeObject" title="PyTypeObject">PyTypeObject</a> <code class="sig-name descname">PyContext_Type</code><a class="headerlink" href="#c.PyContext_Type" title="永久链接至目标">¶</a></dt>
<dd><p>表示 <em>context</em> 类型的类型对象。</p>
</dd></dl>

<dl class="var">
<dt id="c.PyContextVar_Type">
<a class="reference internal" href="type.html#c.PyTypeObject" title="PyTypeObject">PyTypeObject</a> <code class="sig-name descname">PyContextVar_Type</code><a class="headerlink" href="#c.PyContextVar_Type" title="永久链接至目标">¶</a></dt>
<dd><p>表示 <em>context variable</em> 类型的类型对象。</p>
</dd></dl>

<dl class="var">
<dt id="c.PyContextToken_Type">
<a class="reference internal" href="type.html#c.PyTypeObject" title="PyTypeObject">PyTypeObject</a> <code class="sig-name descname">PyContextToken_Type</code><a class="headerlink" href="#c.PyContextToken_Type" title="永久链接至目标">¶</a></dt>
<dd><p>表示 <em>context variable token</em> 类型的类型对象。</p>
</dd></dl>

<p>类型检查宏：</p>
<dl class="function">
<dt id="c.PyContext_CheckExact">
int <code class="sig-name descname">PyContext_CheckExact</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *o</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_CheckExact" title="永久链接至目标">¶</a></dt>
<dd><p>如果 <em>o</em> 的类型为 <a class="reference internal" href="#c.PyContext_Type" title="PyContext_Type"><code class="xref c c-data docutils literal notranslate"><span class="pre">PyContext_Type</span></code></a> 则返回真值。 <em>o</em> 必须不为 <code class="docutils literal notranslate"><span class="pre">NULL</span></code>。 此函数总是会成功执行。</p>
</dd></dl>

<dl class="function">
<dt id="c.PyContextVar_CheckExact">
int <code class="sig-name descname">PyContextVar_CheckExact</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *o</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextVar_CheckExact" title="永久链接至目标">¶</a></dt>
<dd><p>如果 <em>o</em> 的类型为 <a class="reference internal" href="#c.PyContextVar_Type" title="PyContextVar_Type"><code class="xref c c-data docutils literal notranslate"><span class="pre">PyContextVar_Type</span></code></a> 则返回真值。 <em>o</em> 必须不为 <code class="docutils literal notranslate"><span class="pre">NULL</span></code>。 此函数总是会成功执行。</p>
</dd></dl>

<dl class="function">
<dt id="c.PyContextToken_CheckExact">
int <code class="sig-name descname">PyContextToken_CheckExact</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *o</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextToken_CheckExact" title="永久链接至目标">¶</a></dt>
<dd><p>如果 <em>o</em> 的类型为 <a class="reference internal" href="#c.PyContextToken_Type" title="PyContextToken_Type"><code class="xref c c-data docutils literal notranslate"><span class="pre">PyContextToken_Type</span></code></a> 则返回真值。 <em>o</em> 必须不为 <code class="docutils literal notranslate"><span class="pre">NULL</span></code>。 此函数总是会成功执行。</p>
</dd></dl>

<p>上下文对象管理函数:</p>
<dl class="function">
<dt id="c.PyContext_New">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *<code class="sig-name descname">PyContext_New</code><span class="sig-paren">(</span>void<span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_New" title="永久链接至目标">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>创建一个新的空上下文对象。 如果发生错误则返回 <code class="docutils literal notranslate"><span class="pre">NULL</span></code>。</p>
</dd></dl>

<dl class="function">
<dt id="c.PyContext_Copy">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *<code class="sig-name descname">PyContext_Copy</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *ctx</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_Copy" title="永久链接至目标">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>创建所传入的 <em>ctx</em> 上下文对象的浅拷贝。 如果发生错误则返回 <code class="docutils literal notranslate"><span class="pre">NULL</span></code>。</p>
</dd></dl>

<dl class="function">
<dt id="c.PyContext_CopyCurrent">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *<code class="sig-name descname">PyContext_CopyCurrent</code><span class="sig-paren">(</span>void<span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_CopyCurrent" title="永久链接至目标">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>创建当前线程上下文的浅拷贝。 如果发生错误则返回 <code class="docutils literal notranslate"><span class="pre">NULL</span></code>。</p>
</dd></dl>

<dl class="function">
<dt id="c.PyContext_Enter">
int <code class="sig-name descname">PyContext_Enter</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *ctx</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_Enter" title="永久链接至目标">¶</a></dt>
<dd><p>将 <em>ctx</em> 设为当前线程的当前上下文。 成功时返回 <code class="docutils literal notranslate"><span class="pre">0</span></code>，出错时返回 <code class="docutils literal notranslate"><span class="pre">-1</span></code>。</p>
</dd></dl>

<dl class="function">
<dt id="c.PyContext_Exit">
int <code class="sig-name descname">PyContext_Exit</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *ctx</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_Exit" title="永久链接至目标">¶</a></dt>
<dd><p>取消激活 <em>ctx</em> 上下文并将之前的上下文恢复为当前线程的当前上下文。 成功时返回 <code class="docutils literal notranslate"><span class="pre">0</span></code>，出错时返回 <code class="docutils literal notranslate"><span class="pre">-1</span></code>。</p>
</dd></dl>

<dl class="function">
<dt id="c.PyContext_ClearFreeList">
int <code class="sig-name descname">PyContext_ClearFreeList</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_ClearFreeList" title="永久链接至目标">¶</a></dt>
<dd><p>Clear the context variable free list. Return the total number of
freed items.  This function always succeeds.</p>
</dd></dl>

<p>上下文变量函数:</p>
<dl class="function">
<dt id="c.PyContextVar_New">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *<code class="sig-name descname">PyContextVar_New</code><span class="sig-paren">(</span>const char<em> *name</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *def</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextVar_New" title="永久链接至目标">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>创建一个新的' ' ContextVar' '对象。形参*name*用于自我检查和调试目的。可选形参*def*为上下文变量指定默认值。如果发生错误，这个函数返回' ' NULL ' '。</p>
</dd></dl>

<dl class="function">
<dt id="c.PyContextVar_Get">
int <code class="sig-name descname">PyContextVar_Get</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *var</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *default_value</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> **value</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextVar_Get" title="永久链接至目标">¶</a></dt>
<dd><p>获取上下文变量的值。如果在查找过程中发生错误，返回' ' -1 ' '，如果没有发生错误，无论是否找到值，都返回' ' 0 ' '，</p>
<p>如果找到上下文变量，<em>value</em> 将是指向它的指针。 如果上下文变量 <em>没有</em> 找到，<em>value</em> 将指向：</p>
<ul class="simple">
<li><p><em>default_value</em>，如果非``NULL``;</p></li>
<li><p><em>var</em> 的默认值，如果不是 <code class="docutils literal notranslate"><span class="pre">NULL</span></code>；</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">NULL</span></code></p></li>
</ul>
<p>如果找到该值，函数将创建对它的新引用。</p>
</dd></dl>

<dl class="function">
<dt id="c.PyContextVar_Set">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *<code class="sig-name descname">PyContextVar_Set</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *var</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *value</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextVar_Set" title="永久链接至目标">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>在当前上下文中将 <em>var</em> 的值设为 <em>value</em>。 返回指向 <a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyObject</span></code></a> 对象的指针，如果发生错误则返回 <code class="docutils literal notranslate"><span class="pre">NULL</span></code>。</p>
</dd></dl>

<dl class="function">
<dt id="c.PyContextVar_Reset">
int <code class="sig-name descname">PyContextVar_Reset</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *var</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *token</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextVar_Reset" title="永久链接至目标">¶</a></dt>
<dd><p>将上下文变量 <em>var</em> 的状态重置为它在返回 <em>token</em> 的 <a class="reference internal" href="#c.PyContextVar_Set" title="PyContextVar_Set"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyContextVar_Set()</span></code></a> 被调用之前的状态。 此函数成功时返回 <code class="docutils literal notranslate"><span class="pre">0</span></code>，出错时返回 <code class="docutils literal notranslate"><span class="pre">-1</span></code>。</p>
</dd></dl>

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